1. Field of the Invention
The present invention relates to recording apparatuses that are configured to execute a plurality of detecting operations for a recording operation using an optical sensor and control methods.
2. Description of the Related Art
Conventional inkjet recording apparatuses (hereafter simply called recording apparatuses) generally include various detection or measurement sensors for various purposes in order to improve the image quality, accuracy, user friendliness, etc. For example, a sensor configured to detect the width (size) of a recording sheet (also referred to as a recording medium) set in the recording apparatus or the position of an edge of the recording sheet, a sensor configured to measure the density of a patch (pattern) or an image recorded on the recording sheet, etc., are provided. In addition, a sensor configured to detect the thickness or the presence/absence of the recording sheet, a sensor for determining the kind of the recording sheet, etc., are provided.
The edge detection of the recording sheet is useful for accurate printing in a print area of the recording sheet. In particular, high-accuracy detection is useful in marginless printing. A typical sensor configured to detect an edge of a recording sheet includes a single light-emitting element and a single light-receiving element that form a reflective optical system, and the edge can be detected on the basis of a change in a reflection intensity.
Optical sensors are often installed in recording apparatuses. A typical optical sensor includes a light-emitting element for emitting light and a light-receiving element for receiving the light emitted from the light-emitting element, and outputs an output value corresponding to the amount (intensity) of light received by the light-receiving element. As examples of optical sensors, transmissive and reflective sensors are often used.
The reflective sensors can be configured for detecting the thickness of a recording sheet. In an example of a reflective sensor, a light-emitting element and a light-receiving element can be arranged such that light is emitted from the light-emitting element toward the surface of the recording sheet, which is a detection object, is reflected by the recording sheet, and is received by the light-receiving element. The distance from the reflective sensor to the surface of the recording sheet can be determined on the basis of the amount of light received by the light-receiving element or the position of light received by the light-receiving element. When, for example, an optical reflective sensor is disposed on a carriage, the recording sheet, which is a detection object, is fed from a recording sheet holder and is placed on a platen. The distance between the reflective sensor disposed on the carriage and the platen is already known from the design of the recording apparatus. Therefore, the thickness of the recording sheet can be detected if the distance between the reflective sensor and the surface of the recording sheet can be determined.
Japanese Patent Laid-Open No. 05-087526 discusses a structure in which an LED or a semiconductor laser can be used as the light-emitting element in a sensor configured to detect the thickness of a recording sheet. In this structure, a position sensitive detector (PSD) or a CCD can be used as the light-receiving element. According to this publication, light emitted by the light-emitting element is reflected by a measurement object, and a part of the reflected light is received by the light-receiving element. In this structure, when the distance between the optical sensor and the measurement object varies, the center position of the reflected light received by the light-receiving element varies accordingly. When the light-receiving element is a CCD, the amount of light can be measured for each pixel. Therefore, the center position of the reflected light can be determined by detecting the pixel at which the amount of light has a peak, and the distance between the optical sensor and the measurement object can be calculated by triangulation. In addition, when the light-receiving element is the PSD, the center position of the reflected light received by the light-receiving element can be calculated from two outputs that vary in accordance with the center position of the reflected light, and the distance between the sensor and measurement object can be calculated from the center position by triangulation.
On the other hand, an example of a sensor configured to detect the width or an edge (leading or trailing edge) of a recording sheet includes a single light-emitting element and a single light-receiving element that form a reflective optical system, and the edge can be detected on the basis of a change in a reflection intensity (amount of reflected light). The intensity of light received by the light-receiving element differs between the case in which light emitted from the light-emitting element is reflected by the surface of the recording sheet and the case in which the light emitted from the light-emitting element reflected by members for example a platen or a conveying path that are different from the recording sheet. Therefore, it can be determined whether or not the recording sheet is placed in a detection area of the optical sensor in accordance with the intensity of the reflected light. In an inkjet recording apparatus, a carriage is moved in a direction different from the direction in which the recording sheet is conveyed. Therefore, the longitudinal edges, which are different from the leading and trailing edges, of the recording sheet can also be detected by placing the reflective sensor on the carriage.
As examples of sensors configured to measure a color density of a patch printed on a recording sheet, a sensor including three light-emitting elements for red, blue, and green and a single light-receiving element and a sensor including a white light source and a light-receiving element having a color filter are known. Japanese Patent Laid-Open No. 05-346626 discusses a method for obtaining the color density using such a sensor, in which light is incident on the color patch, reflected by the color patch, and received by the light-receiving element. According to this method, the color density is obtained by calculating an amount of reduction in the reflection intensity with respect to a reference reflection intensity. In an inkjet recording apparatus, a carriage is moved in a direction that intersects the direction in which the recording sheet is conveyed. Accordingly, by placing the reflective sensor on the carriage, the density of the patch recorded at any position on the recording sheet can be detected.
Although there are conventional optical sensors that can individually perform respective detecting operations, structures for performing the respective detecting operations largely differ from each other. Therefore, it has been difficult to perform various detecting operations using an integrated sensor unit. In conventional structures, even when, for example, an integrated sensor unit that can perform various detecting operations is obtained, the size of the sensor unit is increased since each of the sensors included therein has a complex optical system. Therefore, the size of a recording apparatus that includes the sensor unit is also increased.